Duct structures and other items allowing fluid flow may have photocatalyst material disposed on the surface to be activated by light from a light delivery system. The efficiency of the photoreactor depends in part on the uniformity of the light illuminating the item as well as the correspondence between the fluid flow profile and an irradiation profile of the light generated by the light delivery system. However, the geometric differences between the shape of the light source and the shape of the surface being illuminated may naturally cause some surfaces to receive more light than other surfaces (e.g., surfaces closer to the light source will have more illumination than surfaces farther from the light source).
Further, the system ideally matches the irradiation profile to the fluid flow profile. A non-uniform irradiance profile and/or a lack of a match between the irradiation profile and the fluid flow profile may result in less than optimum utilization of light energy. Areas experiencing excess fluid flow with respect to the irradiance profile, for example, will have excess target chemical species without sufficient photons in the emitted light to catalyze them. Similarly, areas experiencing low fluid flow will have fewer target chemical species than photons in the emitted light, thus wasting photons. This sub-optimal reactor efficiency occurs regardless of the specific method used to guide photons from the light source (e.g., free-space delivery, total internal reflection, etc.).
There is a desire for a light delivery system and method that can improve the efficiency of photoreactors.